Copolymers of tetrafluoroethylene and fluorovinyl compounds are used in coating metal substrates because of their excellent non-stick properties, chemical resistance, and heat resistance. However, poor adhesion of these copolymers to the substrate is a drawback. Such problems with adhesion have hitherto been addressed by carrying out surface pretreatment such as sandblasting the substrate to roughen it, followed by the coating of a primer. The primer is often a mixture of fluorocarbon resin with adhesion promoters such as heat resistant polymer resin, e.g., polyimide, polyamideimide, polyether sulfone or polyphenylene sulfide.
However, with certain metal substrates, especially stainless steel, even with pretreatment, it has not been easy to obtain a bonding coat which has sufficient water resistance. Further, it is costly and unduly complex to have to perform several coating steps.